Thank you so much all of you!! I am so sorry for my late reply as after I post the message, i check back again next day but can't see my post, so I through there is something wrong with my computer that I can't post it successfully.

It's so nice to join this forum as many of you give me many advises that I didn't think about.

In this month, my son is getting much better, feel like he suddenly grow up a lot, I have tried to leave him for 15-30mins when he is in the parent co-op preschool and he only cry for a while. It is a great improvement, and now I am more confident that he will be fine when he go to preschool by himself later in Sept. Thanks for sharing 2Giftedkids and indigo ^-^

I now arrange some playdate at park (2 playdays with different kids each week) rather than at home, and so he get along with his friends pretty well too, he still have sensory issue with noise, so i think it is the main thing i have to solve it rather than social skill.

EmeraldCity, Thanks for your info, I have read those book too once my son was diagonized with SPD, and they are really helpful ^-^ I am lucky to know that he has SPD in his very young age (20m), otherwise the problem may grow.

Mana, glad to know that your DD grew out of her sensitivities, i think my son also grew out some of his sensitivities too after he join the mommy and me class which provide him lots of sensory activities (e.g. many things he refuse to touch when he was 22m but now he can touch and play with them and he enjoy sand play recently !)

DAD22, thanks for the link too, i also like the independent learning and quite environment of Montessori school. ^-^ My son always freeze up too when teacher teaching new songs and dance, or when some kids are running arround, i think he is really careful and have to observe everything first before he start joining.

Dude, you point out a very important point that i didn't think about when finding preschool. Although my son is a "good boy" in teacher's eyes, he will answer what teacher is asking, and can sit still for a long time but for the toys he play with, he will never play with the "designed way" once he has master it, when he is obsessive with shapes, he use thomas the train to build a pentagon, use crayons to build a parallelogram, etc. Now he like to see the house numbers of each house, so once he has some number puzzle on hands, he will make different "house number" and said "no. 2 is living in house 559" sth like that. Thanks a lot for reminding me to be careful when look for a Montessori school.

I am still looking for a preschool for him, currently a christian preschool which use Montessori materials is my first choice, but this sch has a long waiting list so not sure if he can join it or not.

Thanks a lot ^-^